ML21308A075
| ML21308A075 | |
| Person / Time | |
|---|---|
| Issue date: | 11/08/2021 |
| From: | Michelle Gonzalez NRC/RES/DRA/PRAB |
| To: | |
| Gonzalez, Michelle - 301 415 5661 | |
| References | |
| Download: ML21308A075 (17) | |
Text
Using Operational Experience to Support Dynamic PRA Activities Michelle M. Gonzalez U.S Nuclear Regulatory Commission ANS PSA 2021 November 8, 2021
Outline Introduction/Background Objective Approach Events descriptions and Dynamic Interactions Conclusions Next steps
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Background===
Over the years, Dynamic PRA (DPRA) has been advocated as a potentially useful supplement to commonly used event tree/fault tree methods.
There has been only limited formal investigation of dynamics observed during actual operating events that might be important to consider in a decision that would support the use of DPRA.
Objectives The objective of this work was to describe the status and current results of a limited scope, exploratory, qualitative study that:
Reviews some past nuclear power plant reactor incidents for important dynamic behaviors during the incidents Considers if and how a DPRA might improve on conventional PRA treatments of such features To suggest classes of behaviors that should be considered when performing a DPRA.
The study does not address heavily documented or highly complex nuclear power plant accidents (TMI, Chernobyl, Fukushima Daiichi)
Approach Reviewed individual event reports to identify selected dynamics.
The review focused on the identification and characterization of the system elements and their interactions (e.g. external elements, local environment, operators) 5 events analyzed:
1959 fuel melting accident at the Sodium Reactor Experiment 1985 loss of main feed water at Davis Besse 1989 turbine oil fire at Vandellos 1999 flood incident at Blayais 2020 loss of offsite power at Duane Arnold
Blayais Flooding Event (1999)
Timeline for Blayais Flooding Event Event Description
- Four-unit PWR located on the west coast of France
- Severe winter storm on December 27, 1999
- Units 1,2, and 4 operating at full power
- Unit 3 was refueling
- LOOP to units 2 and 4
- Flood water damaged the dike, failed internal barriers and entered Units 1 and 2
Blayais Flooding Event (1999) Contd No.
Time*
Element 1 Element 2 Interaction 1
0:00 Ext. Env.
Network High winds down trees, damage power lines 3
0:30 Ext. Env.
Loc. Env.
Storm driven waves on top of storm surge and high tide overtop dyke, flood site 4
2:00 Ext. Env.
Network High winds cause grid instability 5
2:00 Network Plant Grid instability leads to loss of 400 kV power to Units 2 and 4, reactor scram, EDGs start and load 6
2:30 Loc. Env.
Plant Site flooding leads to partial loss of Unit 1 ESWS, loss of Unit 1 and Unit 2 LHSI and CSS 7
2:30 Plant Staff Plant Unit 2 400 kV is restored 8
3:00 Ext. Env.
Plant Staff High water level alarm received by Unit 4 9
3:00 Plant Staff High water alert not passed on to other units 10 4:20 Plant Staff Plant Unit 4 400 kV is restored 14 7:50 Plant Staff Arrival of offsite personnel allows activation of Level 1 Emergency Plan 20 14:00 Plant Staff Offsite Orgs.
Level 2 Emergency Plan activated for Unit 1; national emergency teams activated, discuss proposed shutdown strategy considering possibility of additional failures and Y2K complications Selection of Dynamic Interactions During Blayais Flooding Event
Blayais Flooding Event (1999) Contd Commentary Interactions occurred within hours others within days Timeframe information is important when developing a detailed dynamic model Assuming a game over approach, might not be realistic. A dynamic analysis might provide additional insights
Vandellos Turbine Fire (1989)
Event Description Gas cooled, natural uranium fueled, graphite moderated reactor located in Spain Reactor operating at 80% power Series of events after the ejection of 36 blades from Turbine Ejected blades severed a pipe, spilling 4500 liters of lubricating oil in 55 seconds Burning hydrogen ignited the lubricating oil Burning oil damaged expansion joints, spilling significant amounts of sea water, resulting in a flooding in the turbine building Burning oil spread on top of the water Water reached the reactor building Turbo blowers and feedwater pumps for the heat exchangers failed 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> to regain auxiliary feedwater flow to main heat exchangers 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> to extinguish the fire
VandellosTurbine Fire (Contd)
No.
Time Element 1 Element 2 Interaction 1
21:39 Plant Plant Staff Turbine blades ejected 2
21:40 (00:01)
Plant Staff Plant
- 1. Unusual vibrations detected
- 2. Vibration alarm and turbine trip annunciation
- 3. Fire observed in the turbine
- 4. Manual trip of reactor 3
21:40 (00:01)
Plant Internal Hazard (fire)
- 1. 4500 lts of oil spilled from severed pipe
- 2. Hydrogen excursion ignited the lubricating oil (seal failure)
- 3. Sprinkler activated as designed, but did not control fire 4
21:40 (00:01)
Internal Hazard (
Fire)
Internal Hazard (flood)
Fire caused expansion joint damage, spilling water from the circulating water system. Water collected in the basement of the turbine building.
Sump pumps did not activate due to cable damage 5
21:40 (00:01)
Internal Hazard (
Fire)
Plant Staff Fire brigade called 13 4:00 (6:21)
Plant Staff Plant Fire extinguished 14 1:30 (36:00)
Staff Cooling recovered Selection of Dynamic Interactions During Vandellos Turbine Fire
Vandellos Turbine Fire (1989) (Contd)
Commentary Major challenge was the rapid, parallel development of multiple hazards scenarios DPRA provides a framework allowing the treatment of these scenarios To analyze these kind of scenarios, a high-fidelity model would be needed.
Duane Arnold Loss of Offsite Power (2020)
(Contd)
Event Description BWR Reactor, Mark I containment, located in Iowa On August 10, 2020, the plant experienced a loss of offsite power (LOOP) event due to high winds High winds caused damage to 6 offsite power sources LOOP caused a generator trip and automatic reactor scram EDGs provided power to safety-related busses Debris clogged the Train B Emergency Service Water strainer Damage to the Reactor, Turbine and FLEX Buildings
Duane Arnold Loss of Offsite Power (2020)(Contd)
No.
Approx. Time (Interval)
Element 1 Element 2 Interaction 1 (0:00)
External Environment High Winds Storm Derecho 2 11:38 (0:00)
Plant Staff Entered abnormal operating procedures 3 12:35 (0:57)
Network Plant Grid perturbation caused the two EDGs ('A' and 'B' EDGs) to automatically start and run unloaded.
HPCI and RCIC initiated automatically 4 12:46 (1:08)
Plant Load reject and reactor scram 5 12:49 (1:11)
Network Plant LOOP caused a main generator trip on reverse power automatic reactor scram 6 12:58 (1:21)
Plant Staff Licensee declared an unusual event 7 22:30 (11:52)
Plant Staff Plant Shutdown cooling initiated 8 22:40 (12:02)
Plant Staff Plant Operators bypass train B ESW strainer due to high differential plugging 10 11:26 (23:48)
Plant Staff Plant 161 KV off-site power restored 12 13:12 (25:34)
Network Plant Safety bus A reenergized from offsite power 13 13:34 (25:56)
Network Plant Safety bus B reenergized from offsite power Selection of Dynamic Interactions During Duane Arnold Loss of Offsite Power
Duane Arnold Loss of Offsite Power (2020)
(Contd)
Commentary LOOP with and unavailable EDG that can be treated using conventional tools If storm damage would have been more severe, plant staff actions would have been more challenging Dynamic analysis would provide additional useful insights
Conclusions Completed a small-scale exploratory study, analyzing 5 nuclear events.
Identified a number of interactions that Appeared to be important in the evolution of the incidents Appeared to be amenable to direct treatemnt in a DPRA Insights from this small-scale study indicate that the behaviors and interactions identified by conducting a simplified dynamic analysis can point towards other failures and responses that could be modeled in a conventional PRA.
Insights might change as more events are reviewed
Next Steps Complete Complete final report including detailed list of interactions Address Address how the identified dynamic behaviors would be treated in a conventional PRA Analyze Analyze additional events
Questions For further questions, please contact:
Michelle Gonzalez (Michelle.Gonzalez@nrc.gov)